1. Technical Field of the Invention
This invention broadly relates to hydraulic cement compositions. It further and more specifically relates to materials used to disperse particles of hydraulic cement in water. Such materials, when employed in the art of subterranean well cementing and depending upon the desired function of the material, are sometimes referred to as dispersants or as dispersing agents, sometimes as densifiers or as densifying agents, sometimes as viscosity reducing agents and sometimes as friction reducing agents.
The invention also relates to a method of cementing a conduit in a borehole penetrating a subterranean formation comprising the use of a slurry of hydraulic cement in water containing a dispersant.
2. Related Art and Problems Solved
When dry hydraulic cement is mixed with water to form a slurry of cement in water, it has been observed that individual particles of the cement tend to attract, agglomerate or otherwise stick together. Such attraction can result in the prevention of adequate wetting of the cement by the mixing water and thus interfere with the complete hydration reaction between the cement and the water. It has also been observed that the attraction phenomenon can be eliminated or at least reduced and the wettability of the cement increased by adding to the slurry an appropriate quantity of a material which is believed to cause the individual particles of cement in the slurry to repel one another and thus to promote dispersion of the particles in the aqueous phase of the slurry. Such materials are, therefore, called dispersants or dispersing agents.
It has also been observed that a slurry of cement in water in which the individual cement particles are not dispersed has a viscosity greater than a slurry of cement in water in which the individual cement particles are dispersed. Thus, with all parameters remaining identical except for the presence or absence of a dispersant, the viscosity of a cement slurry can be reduced by adding to the slurry an appropriate quantity of a dispersant. For a more complete discussion of dispersion see Well Cementing, Erik B. Nelson (Editor) Chapter 3-7 "Dispersants", pages 3-18 to 3-24, Elsevier Science Publishing Company, Inc., 1990.
In view of the above it is apparent why dispersants have been referred to as viscosity reducers or as viscosity reducing agents; and, further, since viscosity is known to contribute to frictional resistance in fluid flow, it is also apparent why dispersants have been referred to as friction reducers or as friction reducing agents.
In another aspect, since dispersants, as explained above, function to help increase the wettability of individual cement particles, this function enables the use of decreased quantities of mixing water, without change in slurry viscosity, to thereby result in the increase in density of the resulting cement slurry. Accordingly, dispersants have also been referred to as densifiers or as densifying agents.
There is a considerable body of prior U.S. Patents dealing with materials used to disperse particles of hydraulic cement in water. One such patent is U.S. Pat. No. 4,818,288 to Aignesberger and Plank which discloses a dispersant for a salt-containing cement slurry consisting of the condensation product of a ketone, an aldehyde and a compound for introducing acid groups into the condensation product. The preferred compound disclosed in Aignesberger, et al., for introducing acid groups are sulfites and particularly, sodium sulfite.